This work is a continuation of studies on the nephrotoxic nature of Bence Jones proteins (BJP) and the factors important in the genesis of both the acute renal failure associated with BJ proteinuria and the chronic deterioration of renal function seen in myeloma kidney. BJP's are isolated from urine of patients with myeloma and analyzed as to type, group, secondary structure and isoelectric point (pI). Data obtained is correlated to type and extent of renal disease. These proteins are then examined in a rat infusion model under conditions of mild saline diuresis, Na2SO4 diuresis after acid loading, CaCl2 infusion, hydropenia and hypertonic saline infusion and lysosomal enzymuria to determine what physiologic conditions are necessary for expression of nephrotoxicity as expressed by change in functional parameters, immunohistology and renal ultrastructure. In vitro studies on polymer-precipitation of these proteins during partial peptic digestion and co-precipitation with Tamm Horsfall mucoprotein are to determine conditions necessary for urinary cast formation.